The present disclosure relates to an internal combustion engine system comprising an internal combustion engine, an exhaust system, an exhaust gas recirculation circuit and a turbocharger comprising a first turbine interacting with a first compressor for charging air to the internal combustion engine. An exhaust gas recirculation passage is arranged to divert exhaust gases from the internal combustion engine upstream the first turbine and to debouch the exhaust gases downstream the first compressor. The present disclosure also relates to a vehicle comprising such an internal combustion engine system.
It is well known to provide an internal combustion engine with a turbocharger, i.e. with a turbine and a compressor. Certain engines are even provided with a dual stage turbocharger comprising generally a low pressure and a high pressure turbine and a low pressure and a high pressure compressor, both connected in series. The reason for doing so is generally to supply the combustion with more air in order to make the engine more efficient and provide more power.
When driving at high altitude the air pressure produced by the turbocharger for the engine may not be sufficient to provide adequate power to the vehicle. When the engine determines that the vehicle is driving at high altitude, the turbocharger is speeding up to provide more air to the engine. When doing so the turbocharger runs the risk of over speed. Additionally, at higher altitudes ambient air may be so thin that the pressurisation in the turbocharger may still not be sufficient. These high altitudes may be at e.g. 1500 m and up to 3000 m depending on for which part of the world the vehicle is destined. It may be desirable for vehicles to perform equally well, or at least not much poorer at these raised altitudes than at sea level.
An internal combustion engine may also be provided with an exhaust gas recirculation system, an EGR system, in order to lower combustion temperatures and thereby reduce the emissions from the engine. It is well known that fuel reduction and exhaust emissions are two of the major challenges for the present time vehicle development.
For an engine having an EGR system it has also been known to provide it with a turbocharger in which the turbine work is reduced either through throttling or through by-passing the turbine, since otherwise the pressure balance between the intake and the exhaust side of the engine may be disadvantageous for the EGR system. Such a system preferably should have a lower pressure at the intake side of the engine in comparison to at the exhaust side of the engine for successfully delivering a part flow of exhaust gases from the exhaust side to the intake side.
A document disclosing a so called short route EGR in combination with a turbocharger is US 2012/0124992 A1. This document discloses a power source connected to an exhaust passage in which a turbine is connected to a compressor. The power system also discloses an exhaust gas recirculation passage comprising an EGR cooler. The document focuses on regulating the temperature in the EGR cooler in order to better adapt the temperature of the recirculated exhaust gases for proper combustion. This is done through the addition of a second compressor which supplies compressed air to the EGR cooler. The second compressor is either connected to the same turbine as the first compressor, or to a separate second turbine.
It is desirable to further improve the drivability, especially at high altitudes, and to improve the efficiency of the internal combustion engines in vehicles, in particular for heavy duty trucks.
According to a first aspect of the present disclosure an internal combustion engine system is disclosed which comprises an internal combustion engine, an exhaust system, an exhaust gas recirculation circuit and turbocharger comprising a first turbine interacting with a first compressor for charging air to the internal combustion engine. An exhaust gas recirculation passage is arranged to divert exhaust gases from the internal combustion engine upstream the first turbine and to debouch the exhaust gases downstream the first compressor. The internal combustion engine system comprises a bleed air channel which is located to divert compressed air at a location in or downstream from the first compressor and upstream of the internal combustion engine. A second turbine is arranged for receiving bleed air from the bleed air channel to recover energy from the bleed air channel.
By an internal combustion engine system of this kind several advantageous effects are achieved. The positive effects of having a turbocharger and an EGR system are maintained so that an efficient combustion at low temperature in the internal combustion engine is maintained, which in turn results in reduced exhaust emissions. Furthermore the internal combustion engine system also provides good drivability at high altitudes and a good adaptation between driving at normal and at raised altitudes. This is achieved through the use of a first turbine which is used in its whole capacity and which thus is in need of less throttling or other kind of performance reduction means. The possibly redundant capacity, or overcapacity, delivered from the first turbine is instead used in the first compressor to deliver bleed air through the bleed air channel to recover the thus produced redundant energy in the second turbine. As a consequence of this a better utilisation of the capacity of the first turbine is combined with a recovering of energy from it such that better fuel economy is achieved.
Also, since the bleed air channel is located in or downstream the first compressor and upstream the internal combustion engine, and the first compressor is the one delivering compressed air also to the internal combustion engine, a compact internal combustion engine system is achieved, without additional or unnecessary devices which not only are voluminous in a compartment which is very limited in space, but which also adds costs in terms of material, production and maintenance. Finally, such additional devices add friction and the demand for propulsion energy from the internal combustion engine, such that fewer devices will improve the overall efficiency of the system.
According to an embodiment the bleed air channel is directed for heat exchange with a waste heat source originating from the internal combustion engine. The internal combustion engine system produces a fairly extensive amount of energy which is not used for propulsion of the vehicle. This energy is mainly dissipated as heat. This waste heat may preferably be used to deliver energy to other devices of the internal combustion engine system instead of merely be relieved to the ambient. According to this embodiment at least a part of this waste heat is used for heat exchange with the bleed air channel such that this energy may also be recovered in the second turbine.
According to an embodiment the waste heat source is an exhaust gas heat source. A major contributor of waste heat in the internal combustion energy system is the combustion of fuel in the internal combustion engine. When the bleed air channel is made to interact through heat exchange with an exhaust gas heat source of the internal combustion engine an increased recovery of energy may be achieved.
According to an embodiment the waste heat source is the exhaust gas recirculation circuit. Heat exchange with the exhaust gas recirculation circuit means that heat energy therein is at least partially removed and delivered to the bleed air channel, where it may be recovered. The additional effect of this embodiment, on top of the advantage of recovering energy, is that the temperature of the exhaust gases in the exhaust gas recirculation circuit is lowered. Hereby the cooling effect of the exhaust gas recirculation circuit is improved and the combustion temperature in the internal combustion engine will be further lowered. This in turn leads to less emission from the combustion, such as of NOx and soot.
According to an embodiment the waste heat source is any other exhaust gas heat source than the exhaust gas recirculation circuit. Such sources may be the exhaust sys-tern, any exhaust gas after treatment systems connected to the exhaust system, or any other available source of waste heat.
According to an embodiment the exhaust gas recirculation circuit comprises an exhaust gas recirculation cooler, and the bleed air channel is directed through the exhaust gas recirculation cooler for heat exchange therein with the exhaust gases. For improved performance of the exhaust gas recirculation circuit it is advantageous to add an exhaust gas recirculation cooler in order to further cool down the temperature of the exhaust gases which are delivered to the intake manifold of the internal combustion engine. The heat dissipated in the exhaust gas recirculation cooler may thus advantageously be used for heat exchange with the bleed air channel in order to recover the dissipated waste heat. The exhaust gas recirculation cooler is in such a case already located within the internal combustion engine system and it merely entails redesigning it for heat exchange with the bleed air channel to achieve the advantageous effect.
According to an embodiment a regulating valve is located on the bleed air channel for regulating an amount of bleed air through the bleed air channel. Such a regulating valve adds the possibility of regulating the amount of compressed air which is delivered either to the internal combustion engine or to the bleed air channel for recovering of the energy. This way the internal combustion engine system is given the advantage of improved adaptation to ambient conditions, such as the ambient air pressure. When driving at high altitudes, the regulating valve may during extreme conditions fully block any com-pressed air from entering the bleed air channel, such that all compressed air which is available is delivered to the internal combustion engine for proper combustion, such that the power or torque delivered from the internal combustion engine system is keep intact or at least at the highest possible level.
According to an embodiment the second turbine is located downstream of the exhaust gas recirculation cooler.
According to an embodiment the second turbine is arranged to recover energy to the internal combustion engine. When recovering the energy to the internal combustion engine the energy is used for running of the internal combustion engine system, and to the vehicle.
According to an embodiment the second turbine is arranged to convert the recovered energy into mechanical energy. When recovering the energy as mechanical energy it may merely as an example, be delivered to the crank shaft of the internal combustion engine and may thus be used for propulsion of the internal combustion engine system and the vehicle.
According to an embodiment the second turbine is arranged to convert the recovered energy into electrical energy. When recovering the energy as electrical energy it may merely as an example, be delivered to a battery of the internal combustion engine and may thus be used for running of additional devices which are connected to, or located within the internal combustion engine system and the vehicle.
According to an embodiment the second turbine is operatively connected to the internal combustion engine through a gear train. A gear train is a well-known and efficient manner to deliver the energy from the second turbine to the internal combustion engine. It is thus simple to implement.
According to an embodiment the gear train is operatively connected to a torsional damping device. Hereby any power fluctuations from the internal combustion engine are dampened before they reach the second turbine. Such power fluctuation could otherwise damage the second turbine shaft joint. The power fluctuation originates from the fact that the power added to the common transmission from the combustion engine is discontinuous, each combustion implies a discrete step. The power fluctuation mainly originates from fluctuations in exhaust gas pressure from the internal combustion engine.
According to an embodiment the internal combustion engine further comprises a third turbine interacting with a second compressor, the third turbine and the second compressor being arranged to work at a lower pressure than the first turbine and the first compressor. To add a third turbine and a second compressor generally makes the internal combustion engine system into a dual stage turbocharged system. It may thus be possible to add even further amounts of compressed air to the internal combustion engine for improved combustion, and to recover even more energy through expansion in the turbines. The third turbine and the second compressor will work at respective lower pressures than the first turbine and the first compressor. This means that ambient air is firstly drawn into the second compressor and then into the first compressor before entering the internal combustion engine or the bleed air channel. The exhaust gases from the internal combustion engine will similarly firstly pass through the first turbine and secondly through the third turbine before entering any exhaust gas after treatment system or the like and passing out to the ambient. Advantageously, but not necessarily, an intercooler may be located between the second compressor and the first compressor.
According to an embodiment the internal combustion engine further comprises a turbocompound turbine having a gear train for recovering mechanical energy from the exhaust gases, the second turbine being operatively connected to the turbocompound turbine gear train. The turbocompound turbine will interact with the exhaust gases to recover energy therefrom. The turbocompound may come in addition to a third turbine, or as an alternative thereto. Preferably, but not necessarily, it will be located downstream of the first turbine.
According to an embodiment the second turbine is connected to a common gear train with the turbocompound turbine. When the internal combustion system is provide with both a second turbine and a turbocompound turbine, both could be connected to the internal combustion engine system through a gear train. When utilising the same gear train for both turbines, a compact system is achieved.
According to an embodiment bleed air in the bleed air channel and the exhaust gases in the exhaust system are held separated in the exhaust gas recirculation cooler. By holding the bleed air and the exhaust gases separate in the exhaust gas recirculation cooler they do not come into contact with each other. If they do not interact either than through heat exchange this way, the bleed air, which is fresh air from the ambient which has merely been compressed and possibly thus been increased in temperature, is not contaminated by the exhaust gases, which may contain combustion emissions that should be reduced or even better, be completely removed. Hereby the bleed air may be passed generally directly to the ambient after passing the second turbine. Otherwise it would have to be passed through any exhaust gas after treatment system for removal of emissions and that would have put unnecessary increased demands in any such exhaust gas after treatment system.
According to an embodiment the bleed air channel debouches in the exhaust system downstream of any exhaust gas after treatment system connected to the exhaust system. The bleed air is thus not placing larger demands on capacity of the exhaust gas after treatment system.
According to an embodiment the bleed air in the bleed air channel and the exhaust gases in the exhaust system are held separated until the bleed air is made to debouch in the exhaust system downstream of any exhaust gas after treatment system connected to the exhaust system.
According to an embodiment the internal combustion engine further comprises a waste heat recovery heat exchanger located in the exhaust system, and a waste heat recovery circuit having a waste heat recovery turbine for recovering energy from the exhaust gases. Until the exhaust gases originating from the internal combustion engine sys-tern are having the same temperature as the ambient air, there is a potential for recovering this increased temperature to use in the internal combustion engine system in any desired way. A question may be whether this increased temperature is high enough to be worth recovering. If there is a potential for recovering the increased temperature in a manner which is both efficient and does not impart too heavy investments in equipment in the internal combustion engine system it will be advantageous. This embodiment thus includes an additional waste heat recovery heat exchanger, such that the waste heat may be recovered in any desired way.
According to an embodiment the waste heat recovery heat exchanger is located downstream any exhaust gas after treatment system connected to the exhaust system. It may be advantageous to feed the exhaust gas after treatment system with exhaust gases having a raised temperature in order for at least parts of the exhaust gas after treatment system to function properly. Such devices as diesel particulate filters and selective catalytic reduction catalysts are known to operate within certain temperature intervals to deliver the filtering and catalytic effect. When placing the waste heat recovery heat exchanger downstream any such exhaust gas after treatment system the dual effect of maintaining the temperature of the exhaust gases in the exhaust gas after treatment system, and possibly even receiving further heat power from combustion or catalytic processes in the exhaust gas after treatment system to the waste heat recovery heat exchanger is achieved.
According to an embodiment the waste heat recovery turbine is arranged to con-vert the recovered energy into mechanical energy. Mechanical energy may be utilised i.a. as propulsive power in the internal combustion engine system.
According to an embodiment the waste heat recovery turbine is arranged to convert the recovered energy into electrical energy. Electrical energy may be utilised i.a. as charging power in any batteries in the internal combustion engine system.
According to an embodiment the waste heat recovery turbine is operatively connected to the internal combustion engine through a gear train. A gear train is a well-known and efficient manner to deliver the energy from the waste heat recovery turbine to the internal combustion engine. It is thus simple to implement.
According to an embodiment the waste heat recovery turbine is operatively connected to the same gear train as the second turbine. This further improves the compactness of the internal combustion engine system, since more devices may be using an already existing gear train.
According to an embodiment the internal combustion engine further comprises an engine control unit which is arranged to control the regulating valve.
According to an embodiment the engine control unit is arranged to control the regulating valve based on an air demand in the internal combustion engine.
According to an embodiment the engine control unit is arranged to control the regulating valve based on ambient air pressure. Other alternatives is e.g. ambient temperature.
According to a second aspect of the present disclosure a vehicle is disclosed which comprises an internal combustion engine according to any one of the embodiments which are disclosed above. The vehicle of this second aspect will generally receive the same advantages as the corresponding internal combustion engine system.
According to an embodiment the internal combustion engine is a diesel engine. Such internal combustion engines my i.a. run on diesel fuel and dimethyl ether, DME.